last-postmask: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/last-postmask - from package: last-align

You may install the required package with command apt-get install {package}

Error in other languages:
last-postmask: bevel nie gevind nie
last-postmask: comandă negăsită
last-postmask: comando não encontrado
last-postmask: commande introuvable
last-postmask: command not found
last-postmask: käsku ei ole
last-postmask: không tìm thấy lệnh
last-postmask: komanda nerasta
last-postmask: Kommando nicht gefunden.
last-postmask: kommandot finns inte
last-postmask: komut yok
last-postmask: nie znaleziono polecenia
last-postmask: níor aimsíodh an t-ordú
last-postmask: no se encontró la orden
last-postmask: no s'ha trobat l'ordre
last-postmask: opdracht niet gevonden
last-postmask: parancs nem található
last-postmask: perintah tidak ditemukan
last-postmask: príkaz nenájdený
last-postmask: příkaz nenalezen
last-postmask: команда не найдена
last-postmask: командата не е открита
last-postmask: 命令找不到
last-postmask: コマンドが見つかりません